The invention relates to a device for purifying a mercury-containing flue gas, at least comprising dust removing means for removing dust from a flue gas, and a quantity of a regenerable amalgamable material for removing mercury from a flue gas.
From the international patent publication WO 92/16284 is known a filter for removing mercury (Hg) from flue gas, which filter comprises a housing with an inlet opening and an outlet opening for gases for purifying and a filter body. The filter body consists of a large number of layers of a thin metal foil covered with a gold layer, between which layers channels are formed for guiding gases for purifying along these layers. In the known filter electrical heating wires or other means are provided for heating said metal foil and the gold layer deposited thereon to a temperature above 20xc2x0 C. in order to regenerate the filter in situ. During regeneration of the filter air or another gas is preferably guided through said channels.
The known filter is particularly intended for use in combination with a cremation furnace to remove mercury originating from dental fillings. Due to the heating installation required for regenerating the gold foil and the cooling device inherently associated therewith which enables condensation of the mercury coming from the filter and released during regeneration, the filter is expensive to purchase and its complexity makes operation vulnerable. Replacement of the filter body requires disassembly of the electrical heating cables and the filter housing, which may necessitate a prolonged and usually unexpected and therefore undesirable interruption in operations.
The object of the invention is to provide an operationally reliable purifying device for removing mercury from flue gas, which is particularly suitable for use in combination with a cremation furnace, which can be manufactured and operated at relatively low cost and which can be regenerated in simple manner without expensive provisions being required for this purpose or normal operations having to be discontinued for a protracted period.
These objectives are achieved, and other advantages obtained, with a purifying device of the type stated in the preamble, which device is adapted according to the invention for removal therefrom in amalgamated state of the quantity of amalgamable material for the purpose of regenerating this material, wherein the material is provided in a manner such that it can be regenerated in amalgamated state outside the device.
Amalgamable material is here understood to mean any material which is capable of alloying with mercury or of binding with mercury by adsorption; amalgamated state is understood to mean a state in which the material is alloyed with mercury or has bound with mercury by adsorption.
In an embodiment of a purifying device according to the invention the quantity of amalgamable material is a quantity of amalgamable metal which is accommodated in removable manner in a filter housing which is adapted to guide a mercury-containing flue gas through this filter housing and in contact with this metal.
The amalgamable metal is for instance metal selected from the group comprising copper (Cu), silver (Ag) and gold (Au).
In an advantageous embodiment the amalgamable metal is copper (Cu) with sulphur (S) bound thereto, this being obtained for instance from a reaction of copper (Cu) with solid sulphur (S) at a temperature of about 104xc2x0 C. By binding S to Cu the surface of Cu available for amalgamation is enlarged, while the capacity for binding mercury is further increased by the S, which forms the compound mercury sulphide (HgS) with mercury.
It has been found that mercury-containing copper with sulphur bound thereto can be regenerated in simple manner in a vacuum oven at a temperature of about 550xc2x0 C., wherein formed HgS decomposes into Hg and S, and Hg which has been taken up into Cu with the formation of a CuHg alloy is released.
In a subsequent embodiment of a purifying device according to the invention the quantity of amalgamable material is a quantity of inorganic amalgamable material which is accommodated in removable manner in a filter housing which is adapted to guide a mercury-containing flue gas through this filter housing and in contact with this material.
The quantity of inorganic amalgamable material is poured for instance in powder or granule form into a container with a gas-permeable bottom which fits into a filter housing such that flue gas guided through this housing is guided via the bottom of the container through the quantity of amalgamable material, wherein mercury in the flue gas is bound by this material.
In an advantageous embodiment of a purifying device according to the invention the inorganic amalgamable material is a mixture of titanium dioxide (TiO2) and divanadium pentoxide (V2O5), wherein the quantity of V2O5 in the mixture lies for instance in the region of 4-7% by weight, the TiO2 forms a carrier for the V2O5 and/or the carrier of TiO2 and the V2O5 carried thereby is provided by particles with a nominal diameter of about 0.8 mm.
In a device according to the invention the quantity of amalgamable material is accommodated for instance in a laminar flow reactor (LFR) for removing mercury from a mercury-containing flue gas guided in a laminar flow through this reactor in contact with this material.
In a particularly advantageous embodiment the quantity of amalgamable material in a device according to the invention is accommodated in a radial flow reactor (RFR) for removing mercury from a mercury-containing flue gas guided in a radial flow through this reactor in contact with this material.
In a radial flow reactor in a device according to the invention the quantity of amalgamable material is provided in a cylindrical reactor vessel between two internal cylindrical walls, and a flue gas is guided in radial direction from the outer wall through the quantity of amalgamable material to the axis of the cylindrical reactor vessel, wherein a pressure gradient is created over the quantity of amalgamable material which enhances the amalgamation process.
In a very advantageous embodiment of a device according to the invention the dust removing means comprise a cyclone or an electro-filter placed in a conduit system for a mercury-containing flue gas flow upstream in the device relative to the quantity of amalgamable material.
Use of a cyclone, which in this respect should also be understood to mean a multi-cyclone and a rotating particle separator, or an electro-filter makes it possible to filter out dust particles from a flue gas at a relatively short distance from the relevant furnace at a temperature which is so high that the flue gas is not saturated with mercury, and all the mercury present in the gas is therefore carried along further downstream in said conduit system to the amalgamable material present in the device.